There are numerous theories regarding the reasons behind the 4/20 effect in the cannabis stocks, with the most popular one being increased media attention on marijuana in general and marijuana stocks in particular during the March/April timeframe as we head into the annual 4/20 "season"

Typically the MJ stocks start moving upwards in mid-March due to the 4/20 effect

In 2016, here a few stocks which nicely demonstrate how 4/20 serves as a catalyst for the pot sector: